1. Field of the Invention
The present invention relates to monolithic ceramic electronic components, and more particularly, the present invention relates to monolithic ceramic electronic components such as monolithic inductors, monolithic capacitors, and LC combined monolithic components, and a method for manufacturing such a monolithic ceramic electronic component.
2. Description of the Related Art
In recent years, electronic devices operating at high frequencies have become common. Inductors, LC combined components, LR combined components, LCR combined components, and the like, which can operate at gigahertz (GHz) frequencies, are required.
However, in an inductor for high-frequency operation, stray capacitance in parallel with the inductor seriously affects the impedance of the inductor. In particular, at GHz frequencies, small stray capacitance on the order of 0.01 pF to 0.1 pF seriously affects the impedance. Consequently, to achieve a desired characteristic by decreasing the stray capacitance, decreasing the dielectric constant ε of ferrite for a magnetic material is required. Unfortunately, decreasing the dielectric constant ε of ferrite by, for example, 14 to 13 or less is difficult practically because of the structure of ferrite.
Thus, a method for decreasing the dielectric constant by mixing a magnetic material with a material such as a resin and glass having a low dielectric constant has been suggested. In such a magnetic composite that is composed of a magnetic material and a non-magnetic material such as a resin and glass, the particles of the magnetic material are covered with the non-magnetic material to interrupt a magnetic path. As a result, permeability is decreased dramatically.
Japanese Unexamined Patent Application Publication No. 55-52300 discloses porous sintered ferrite having a porosity of 20% to 70% for an electromagnetic wave absorber, the porous sintered ferrite having a low dielectric constant because of its high porosity. Since such a porous sintered ferrite has continuous magnetic paths, the electromagnetic properties of the porous sintered ferrite do not vary steeply. That is, even when the porous sintered ferrite has a high porosity, ferrite grains are magnetically coupled to each other. As a result, the variation in the frequency dispersion of the complex permeability of ferrite decreases compared with that of a ferrite composite prepared by mixing ferrite powder and an insulating material.
Japanese Unexamined Patent Application Publication No. 11-67575 discloses a ceramic electronic component provided with ceramic and inner electrodes disposed within the ceramic, the ceramic having pores with a diameter of 1 μm to 3μm and having a porosity of 3 to 30 percent by volume. The pores can decrease the dielectric constant of the ceramic to improve the impedance characteristics of the ceramic electronic component.
When sintered ceramic such as ferrite includes pores, in forming outer electrodes by applying an electrode paste, the paste diffuses into the inside of the sintered ceramic through the pores. As a result, the outer electrodes subside causing deterioration of the mechanical strength and the electrical connection reliability of the outer electrodes. In addition, since the pores are provided in the entire sintered ceramic, if the sintered ceramic is made of ferrite, the magnetic permeability decreases. Consequently, when the sintered ferrite includes a coil element, leakage flux increases, and thus, high impedance cannot be achieved.